This invention relates to the manufacture of memory disks of the type used in the computer field and, more particularly, to a burnishing head and method of burnishing the surface of a memory disk.
Hard (inflexible) disks are used to store information, typically coded information, utilized for data processing. An advantage of such a disk is that it can provide high-speed random access. That is, one can either write or retrieve information from any selected area on a memory surface of such a disk, without having to serially traverse the full memory space of the disk to have access to a selected memory location. Generally, a hard memory disk is mounted within a disk drive which is akin to a record turntable, in that it includes means for rotation of the disk and means for translating a head across the surface of the disk to provide access to a selected annular track. Typically, a plurality of disks, such as two or four, are mounted on a single spindle in spaced relationship to one another and heads are provided to interact with opposite planar surfaces of each of such disks.
The disks now available for hard disk memory arrangements typically are magnetic disks, i.e., each of the surfaces which is to receive and store information is a magnetic surface, such as provided by a thin magnetic film on a substrate. Moreover, the heads which interact with each of the surfaces are so-called "flying" heads, i.e., they do not touch the surface of the disk during its rotation--rather, they ride on an air bearing between the disk and the head caused by the rotation of the disk at high speed. The head which interacts with the surface typically includes the magnetic coil or other mechanism for interacting through space with the disk surface in a non-contact manner. This prevents both wear of either the head or the disk surface which would be caused by a contact transfer of the information between the two during relative movement.
It will be recognized that if asperities (protrusions and the like) on the disk surface encounter a read/write head during high-speed relative movement between the two, an anomaly will be caused. This anomaly could be, for example, damage to the head or at the least an error in the information transfer. Because of such, it is typical in the manufacture of computer disks to burnish the memory surfaces to remove asperities. This generally is achieved by mounting the disk in an arrangement which rotates the same relative to a head in the same manner that the disk is expected to be rotated relative to a magnetic head in a disk drive. A burnishing head, rather than a magnetic head, is provided in the arrangement for removing the asperities as the disk is rotated. Conventionally, the burnishing head is designed as a flying head which passes over the surface to be burnished with a spacing between the two which is less than the normal spacing between a magnetic head and the magnetic surface of the disk. An example of such an arrangement is that described in Volume 17, No. 10, page 3010 (March 1975) of IBM Technical Disclosure Bulletin.
Flying burnishing heads, because they do fly, do not provide the uniformity of asperity removal that one would like. That is, contact of the burnishing head with the asperities during flying can result in head-disk surface spacing variations and consequent non-uniform removal. Moreover, many of such flying head arrangements have included only one cutting edge positioned to engage an asperity. This exacerbates the nonuniformity problem since the single cutting edge is expected to remove the entire asperity that it encounters. The high resolution required for greater density of recording being desired results in lower spacing between the head and disk and more of a likelihood that asperities in a recording surface will interfere with proper information recording and/or retrieval. Non-contact (flying) burnishing heads simply cannot provide as smooth a recording surface as desired.
In view of the above, some effort has been made to come up with a satisfactory "contact" burnishing head, i.e., one which remains in contact with the disk surface during the burnishing operation. An example of such a head is described in U.S. Pat. No. 4,330,910. Such head includes a planar surface designed to contact the disk surface, which planar surface includes either a single groove or a pair of crossed grooves providing sharp edges for contacting and removing asperities. The resulting construction results in many asperities being contacted by a single cutting edge, with the result that either a protruding asperity is only partially removed and interferes with continued smooth contact between the head and the disk surface or that removal of the asperity causes a slight gouging or the like to occur in the disk surface. That is, since a single cutting edge has to remove the entire asperity, it is not unusual for the large piece of debris caused by the asperity to gouge the magnetic surface, or the removal to be simply a removal caused by engagement between two moving objects, rather than a clean slice and a controlled removal.